Extravasation detector using microwave radiometry

ABSTRACT

A microwave antenna senses the temperature of tissue into which a fluid is to be injected. The fluid is injected by a needle or other vascular entry device connected to a fluid injector by a connector tube. The fluid temperature is measured by a temperature sensor attached to the connector tube. An alarm processor determines whether an extravasation occurs by comparing a temperature discrimination function derived from tissue temperature taken at different times with a calculated threshold value. The threshold value is calculated from the tissue temperature and the fluid temperature. The threshold value is recalculated and updated continuously during the fluid injection.

FIELD OF THE INVENTION

This invention relates generally to the field of medical devices fordetecting extravasations in fluid injections. More specifically, thisinvention provides an alarm circuit which compares tissue temperaturewith thresholds calculated from the fluid and tissue temperatures.

BACKGROUND

It is a well known medical procedure to inject a patient with fluids vianeedle or catheter devices. The needle may be connected to a fluidinjector by a connector tube which transmits fluid to the needle. Theconnector tube may also draw fluids from a container such as an IV bag.In such fluid injections detecting the presence of extravasations orinfiltrations of nonvascular tissue is necessary. Extravasations orinfiltrations are detected by measuring temperature changes whichtrigger an alarm condition upon detection of a predetermined temperaturedeviation from normal skin temperature.

Present systems for detecting extravasations are useful in IV druginfusion applications where the flow rate is slow enough such that thefluid is at room temperature when it is injected. The present methodsthus assume a significant and relatively constant difference betweenfluid temperature and limb temperature.

However, with regard to computed tomography ("CT") contrast injectionapplications, where the flow rates from the fluid injector are in therange of 0.1 to 10 ml/s, the response time for temperature sensing is asignificant consideration. A current extravasation detector employs anantenna and radiometer to measure the temperature of the subcutaneoustissue where fluid is injected. An alarm processor uses an algorithm todetermine alarm conditions. The algorithm measures the temperaturesignal periodically and compares it to a fixed threshold level. Theextravasation detector system's alarm processor communicates with thefluid injector so the start of the injector and the fluid flow rate areknown by the alarm processor. The processor records the temperaturesignal at the start of the injection. The alarm processor will signal analarm if the magnitude of deviation from the initial signal exceeds apredetermined magnitude threshold. The magnitude thresholds are takenfrom tables stored by the processor. The threshold values arepredetermined as a function of flow rate and the values are stored inthe tables. The alarm signal allows the processor to shut down the fluidinjector to prevent further extravasations.

However, additional problems are inherent in temperature sensing inextravasation detection. In CT contrast injections, the fluid isusually, but not always, warmed to a temperature near body temperature.The fluid in the connector tube and the connector tube itself areusually at room temperature. Normally, cold fluid is initially injected,followed by warmer fluid. The cold fluid may cause false positivealarms, as a small amount of cold fluid in a blood vessel can cause asignal change identical to that of a larger amount of warmerextravasated fluid. Furthermore, using preset thresholds does notaccount for variations in initial patient limb temperature norvariations in fluid temperature during the injection.

Recent passive patient measurement data indicate that limb temperaturevaries more than had been previously expected. Fluid at 37 degreesCelsius, which is the nominal body temperature, may be warmer than thelimbs of most patients. This difference affects the magnitude thresholdsfor any extravasation decision criteria. Additionally, severalpatient-specific factors may be useful in setting thresholds to minimizefalse alarms (false positives) while being sensitive to trueextravasations. However, predetermined thresholds cannot take thesepatient-specific factors into account.

Thus, an extravasation and infiltration detection device is needed whichcan detect true extravasations in high flow injection situations.Furthermore, a detection device is needed which can detect trueextravasations despite patient variation and temperature changes.

SUMMARY OF THE INVENTION

The invention includes a system for detecting extravasations in tissueinjected with fluid from a fluid injector. A fluid temperature sensorsenses the temperature of fluid present in a connector tube whichtransmits fluid to a patient. The fluid temperature sensor generates afluid temperature signal in response to the fluid in the connector tube.A tissue temperature sensor senses the temperature of the tissueproximate to the site of the injection, and generates a tissuetemperature signal in response.

A processor receives the tissue temperature signal and the fluidtemperature signal. The processor activates an alarm circuit, whichdeclares the occurrence of an extravasation, as a function of the tissuetemperature signal and the fluid temperature signal during the fluidinjection.

A further embodiment of the fluid temperature sensor is used inconjunction with a fluid needle and a fluid connector tube containingfluid. A connector having an interior sidewall connects the tube to theneedle. The fluid temperature sensor has a temperature transducer and ametal insert. The metal insert extends through the connector and theinterior sidewall. The metal insert is adaptable to be in contact withfluid in the connector tube to provide a temperature conductive path,and is coupled to the temperature transducer.

The invention also includes a method of detecting extravasations intissue injected with fluid from a fluid injector. The temperature offluid present in a connector tube transmitting fluid to a patient isperiodically sensed. A fluid temperature signal is generated in responseto the temperature of the fluid. The temperature of tissue proximate thesite of injection is periodically measured and a tissue temperaturesignal is generated. The fluid temperature signal and the tissuetemperature signal are received and a fluid temperature and a tissuetemperature are derived from the received signals. The fluid and tissuetemperatures are stored. The occurrence of an extravasation is declaredas a function of the tissue temperature signal and the fluid temperaturesignal during the fluid injection.

Numerous other aspects and advantages of the present invention willbecome apparent from the following drawings and detailed description ofthe invention and its preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating a prior art system forsensing extravasations,

FIG. 2 is a schematic block diagram of an embodiment of the presentinvention in which a clip-on sensor is used for sensing fluidtemperature,

FIG. 3 is a schematic block diagram of an embodiment of the presentinvention in which a clip-on antenna is used for sensing fluidtemperature extravasations,

FIG. 4 is a schematic diagram of an embodiment of the present inventionin which an in-line sensor is used for sensing fluid temperature,

FIG. 5 is a side elevational view of a temperature sensor and fluidconnector used in the present invention,

FIG. 6 is an coaxial sectional view taken substantially along line 6--6of FIG. 5,

FIG. 7 is a front view of a temperature sensor and fluid connector usedin the present invention,

FIG. 8 is an axial sectional view of an alternative temperature sensoraccording to the invention,

FIG. 9 is a chart showing the factors taken into consideration in aneural net analysis of specific patient factors according to theinvention,

FIG. 10 is a flow diagram of an algorithm according to the presentinvention used to determine alarm threshold levels and to detectextravasations,

FIG. 11 is a graph illustrating the radiometer output versus fluidtemperature at the start of injection,

FIG. 12 is a graph illustrating the radiometer output versus fluidtemperature twenty seconds after injection,

FIG. 13 is a flow diagram of the various modes of operation according tothe present invention,

FIG. 14 is a schematic block diagram of an embodiment of the presentinvention in which a heating/cooling element is attached to theconnector between a needle and a tube,

FIG. 15 is a schematic diagram of an embodiment of the present inventionin which a microwave antenna is used for sensing fluid temperature andfor heating the injected fluid, and

FIG. 16 is a flow diagram of a modified algorithm according to thepresent invention used to determine alarm threshold levels and to detectextravasations.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a block diagram of a prior art sensing system indicatedgenerally at 12 which is useful for detecting extravasations orinfiltrations in fluid injection procedures where the fluid is at ornear room temperature and the injection rate is low. The sensinghardware in system 12 employs a strategy of comparing the magnitude oftissue temperature with predetermined fixed thresholds. In the system12, a needle 16 or other vascular entry device is inserted into a veinin a patient's limb 14. Needle 16 is attached to a connector tube 18,which in turn is connected to a syringe 22. A plunger (not shown) ofsyringe 22 is slidably displaced within the body of syringe 22 by apiston (not shown) of an injector head 20. Injector head 20 in turn iscoupled to a fluid injector 24 by a signal line 25.

The syringe 22 and connector tube 18 are filled with fluid and theneedle 16 is placed in the patient's vein. The fluid injector 24 iscontrolled by a user interface 32 which allows the user to program theinjector 24 with the proper flow rate and total volume of fluid to beinjected into the patient.

An antenna 26 is placed on the patient's limb 14 near the tip of theneedle 16. The antenna 26 receives microwave energy from subcutaneoustissue near the site of injection. A radiometer 28 amplifies the inputfrom the antenna 26 and compares the input to an internal reference. Theoutput of the radiometer 28 is a voltage proportional to the temperaturedifference between the tissue and the radiometer's internal reference. Atypical sensitivity is about 0.3 volts per degree Celsius.

An alarm processor 30 has a radiometer input 34 and a fluid injectorinput 36. Radiometer input 34 is connected to the temperature output ofthe radiometer 28. The radiometer 28 receives power and controlfunctions from a radiometer processor through electrical connections(not shown). Fluid injector input 36 is connected to the injector 24 andcarries signals representing the flow rate of the fluid and the start offluid injection. The alarm processor 30 uses a microprocessor (notshown) to read the temperature signal from the radiometer 28 and theflow rate and the start of fluid injection from the fluid injector 24 todetermine the magnitude threshold values. The threshold values arestored in a table, and the proper threshold value is selected by thealgorithm based on the rate of fluid flow. If the magnitude of thetemperature from the radiometer input 34 exceeds the predeterminedthreshold selected from the stored table, an extravasation orinfiltration is declared.

In an alternate prior art system, the slope of the temperature changeper unit time is compared with a second set of alarm thresholds andprovides a further basis for declaring that an extravasation hasoccurred. The alarm processor 30 halts the fluid injector 24 via acontrol signal through a control output 38. The prior art system 12 islimited in that the use of stored, time-invariant thresholds may resultin false infiltration and unnecessary interruptions in procedure.

FIG. 2 shows a block diagram of a fluid injector system 42 according toa first embodiment of the present invention. Similar to the prior artsystem above, a needle 46 is inserted in a patient limb 44 to transmitfluid into a blood vessel. The fluid is transmitted to the needle 46 viaa connector tube 48 from a syringe 52, which in turn is mounted on aninjector head 50. The injector head 50 is controlled by a fluid injector54. A user may control the start of the fluid flow, the flow rate andthe volume of fluid injected through a user interface 56. User interface56 may also be used to enter patient parameters and select one of aplurality of modes of operation, as will be discussed below. The fluidinjector 54 senses action and position of the parts of injector head 50,such as piston displacement and motor current, and also produceselectrical signals indicating that the fluid has begun to flow, the flowrate and the volume of fluid injected.

Extravasations and infiltrations of subcutaneous tissue may be detectedduring the injection process via an antenna 58 which is placed near thetip of the needle 46. A radiometer 60 is connected to the antenna 58which amplifies the microwave emissions received by the antenna 58. Theradiometer 60 amplifies the signal and produces a voltage outputproportional to the difference between subcutaneous tissue temperatureand an internal reference. While microwave radiometry is preferred inthis embodiment because it can respond more quickly to subsurface tissuetemperature variations than a surface temperature sensor can, the use ofa surface temperature sensor is a viable alternative embodiment, and maybe indicated because of decreased costs and increased ease of use.

A clip-on temperature sensor 76 is clipped on the connector tube 48,preferably near the patient limb 44. The clip-on temperature sensor 76is a temperature measuring transducer such as a thermocouple, or othertemperature sensing element such as a thermistor, which is pressedagainst the outside of connector tube 48 by the clip. The temperaturesensor 76 measures the temperature of the outside of the connector tube48, which is related to the temperature of the fluid injected. There isa time delay due to the thermal mass and low thermal conductivity of theconnector tube 48. The output of temperature sensor 76 is connected tofluid temperature input 70 of alarm processor 62. The fluid temperaturesensor instead may be incorporated into or mounted on the syringe 52, orat a catheter tip within the catheter, to sense the temperature of thefluid at these alternative points.

An alarm processor 62 has a processor 64 (such as a microprocessor) anda memory 66. The memory 66 stores the extravasation algorithm which willbe described below. The memory 66 also stores various input data such astissue temperature, fluid temperature, fluid flow etc. used by theextravasation algorithm. Memory 66 may be Random Access Memory (RAM),magnetic medium or other memory devices. The alarm processor 62 has atissue temperature input 68, a fluid temperature input 70, and a fluidinjector input 72, which are connected to the processor 64. The inputs68 and 70 receive electrical signals representative of tissue and fluidtemperature, respectively. Signals from the fluid injector 54representing the beginning of fluid flow, fluid flow rate and fluidvolume are transmitted to the alarm processor 62 via the fluid injectorinput 72 through a fluid injector input line 71. The processor 64controls the flow of fluid from syringe 52 via a control output 74connected to fluid injector 54 by control output line 73.

FIG. 3 is a block diagram of a second embodiment of the presentinvention indicated generally at 82. Like elements have numbersidentical to their counterparts in FIG. 2. A microwave antenna 84 isattached to the connector tube 48 near the patient limb 44 by aconnector device such as a clip (not shown). The antenna 84 is connectedvia a line 85 to a multiplexor 86 in radiometer 60. Multiplexor 86 isalso connected to antenna 58 via a signal line 87 and outputs either thesignal from antenna 58 representing tissue temperature, or the signal ofantenna 84 representing fluid temperature to the remainder of radiometer60. The radiometer 60 synchronously demodulates the output of themultiplexor 86 into two outputs which are connected to the tissuetemperature input 68 and the fluid temperature input 70 of the alarmprocessor 62. Since its signal is directly related to the temperature ofthe fluid itself, the antenna 84 provides a quick signal response to thefluid temperature in the connector tube 48. In this arrangement, thereis no time delay for heat to be conducted through the tubing wall. Themultiplexor arrangement may be replaced with a second radiometer (notshown) which would be connected to antenna 84 and input 70.

FIG. 4 is a schematic block diagram of a third embodiment 92 of thepresent invention where like elements have identical numbers to theircounterparts in FIG. 2. An in-line temperature sensor 94 is insertedinto the connector tube 48 near the patient limb 44. The temperaturesensor 94 has a thermistor 96 embedded in a plastic piece 98. The sensor94 is coated by a thin protective layer of plastic which is wetted bythe fluid in tube 48. The sensor 94 is preferably disposable and may bereplaced for each different injection; it therefore does not have to bemade to be as durable as a non-disposable sensor.

FIGS. 5-7 show an alternate temperature sensor which may replace thetemperature sensor 76 in FIG. 2. The connector tube 48 is connected tothe needle 46 via a connector indicated generally at 100 which has athreaded collar 102 for receiving needle 46. A thermally conductiveinsert such as metal piece 104 is inserted into a sidewall 101 of theconnector 100. Metal piece 104 serves to quickly conduct heat from thefluid to a clip on temperature transducer 105 which may be a thermistor,thermocouple, black body radiometer or the like. The metal piece 104eliminates the time delay of heat conducted through the relativelyheat-insulative connector tube 48. An alternative to the metal piece 104is shown in FIG. 8, which shows the use of a short metal tube section106 in place of connector 100. Tube 106 is inserted into the length ofthe connector tube 48 and preferably as close to the patient orpossible. A temperature sensor, such as a thermistor 108, could bebonded to the exterior sidewall of tube 106.

The different sensors described above all serve to provide the alarmprocessor 62 with the temperature of the injected fluid near the entrypoint of the needle into the patient limb 44. The system 42 in FIG. 2thus provides continuous data regarding tissue temperature and fluidtemperature to the alarm processor 62 and thus allows the alarmprocessor 62 to adjust the alarm thresholds in real time.

The extravasation detection algorithm run by the processor 64 of thealarm processor 62 adjusts at least one and preferably two alarmthresholds depending on the fluid and tissue temperatures. If thedifference between fluid and tissue temperature is large, the thresholdsshould be large. Otherwise the filling of a normal vein with cold fluidcould falsely trigger the alarm. When the temperature difference betweenfluid and tissue temperature is small, then the thresholds must be attheir minimum to provide the protection required. The subcutaneoustissue temperature taken from antenna 58 is stored in memory 66 and isconstantly compared with updated thresholds by the alarm processor 62.If the tissue temperature or a function determined by the tissuetemperature exceeds a calculated threshold (indicating an extravasationor infiltration) at a given time, the processor 62 sends a signal viathe control signal output 74 to the injector head 54 to stop theinjection. The signal output 74 may also activate user interface 56 toalert the user that an extravasation or infiltration has occurred.Typically, threshold values are updated every 0.1 sec. during a 50second injection using a flow rate of 3 ml/sec. Obviously, differentflow rates will determine different update rates of the thresholdvalues.

The threshold values may be asymmetric. If it is known that the fluid iswarmer than the tissue, then the threshold for a temperature increasecould be less than for a temperature decrease, or a temperature decreasecould be ignored altogether. Additionally, the algorithm provides athreshold minimum (R_(min).sbsb.--_(T)) below which the system cannot gowithout having an unacceptable rate of false positives. The alarmprocessor 62 then alerts the user that the temperature differencebetween tissue and fluid temperatures is too low for reliableextravasation detection.

An additional feature of the present invention is to allow an operatorto input data relating to the patient which may affect the thresholdvalues chosen by the alarm processor 62. These data are typically storedin the memory 66 of the alarm processor 62 for later use by theextravasation detection algorithm. One method of modifying the thresholdvalues is to allow the user to select among several discrete levels ofsensitivity. The operator can base this judgment on factors whichinfluence the likelihood of extravasation, such as patient age, weakenedveins, general health, depth of veins, size or diameter of veins,obesity, type of the vascular entry device used, the difficultyinserting the vascular entry device into the vein, and confidence thatthe needle is properly positioned. Other specific procedural,physiological or anatomical information may be considered.

The above factors (hereinafter sometimes referred to as "PatientParameters") which may influence the threshold values are determined bydata gathered through clinical experience. The flexibility of selectingthese factors employs the operator's judgment in balancing thelikelihood of false positives against the likelihood of false negatives(where an extravasation occurs but the alarm does not occur).

After enough data are collected from clinical experience, a modifiedthreshold selection algorithm could be incorporated in the alarmprocessor 62. The operator can answer questions about the patientthrough a user interface. An algorithm, either one that is deterministicor that has the ability to learn over many injections, then modifies thestandard thresholds using the patient specific parameters. FIG. 9 is achart of the factors which may be processed by a neural network toinfluence the threshold values.

FIG. 10 is a flow diagram indicated generally at 110 of the algorithmused by the alarm processor 62 to determine threshold levels and toactivate the alarm signal to the injector 54. As will be appreciated bythose skilled in the art, other algorithms may be used.

The flow diagram 110 begins with step 112 at which Patient Parameters P₁. . . n are input. As explained above, these may be factors such asgeneral health, depth of veins, size or diameter of veins, or obesity.The Patient Parameters P₁ . . . n may be entered into the processor 64of the alarm processor 62 (see FIG. 2) by the operator. In step 114, theprogrammed flow rate, F_(o), is input by the operator and stored inmemory 66 for use. The programmed flow rate is an initial estimate usedfor the delivered fluid. In step 116, the processor 64 or the userselects one of at least three cases (simple temperature difference, timedelayed temperature difference, or at least one other algorithm fittingwithin the general case of a temperature discrimination function) whichin turn determines the proper calculations to use to calculate initialand updated threshold temperature values. In step 118, the initial fluidtemperature, T_(f).sbsb.o, and initial tissue temperature, T_(s).sbsb.o,are then taken from fluid temperature input 70 and tissue temperatureinput 68 respectively. These values are stored in memory 66 for use bythe algorithm as will be described below. In step 120, the initialpositive and negative alarm threshold values, R_(alarm).sbsb.--_(pos)and R_(alarm).sbsb.--_(neg), are established as functions of patientparameters, P₁ . . . n, injection flow rate F, and the initial tissuetemperature and fluid temperatures. The positive and negative thresholdvalues allow for asymmetric threshold settings which account forasymmetrical physiological responses. The positive and negativethreshold alarms may be established according to the functions describedbelow in conjunction with step 146.

In step 122, the injector head input 72 is checked to determine whetherthe fluid injection has commenced. If the fluid injection has notcommenced, the algorithm loops back to step 118 and measures tissue andfluid temperature again to perform step 120 to update the initial alarmthreshold values. If the fluid injection has commenced, step 124 isperformed to check injector head input 72 to determine whether the fluidinjection has been completed. If the fluid injection is complete, thealgorithm branches to step 126 and ends. If the fluid injection has notbeen completed, the absolute value of the difference between the fluidand tissue temperature is taken and compared with the minimal differencethreshold, R_(min).sbsb.--_(T) in step 128. The minimal differencethreshold R_(min).sbsb.--_(T) is a predetermined constant or may be afunction of some of the patient parameters. For example for a typical CTinjection,. the minimal difference threshold R_(min).sbsb.--_(T) has avalue of 1° C. If the absolute value of the difference of the fluid andtissue temperatures is less than the minimal difference thresholdR_(min).sbsb.--_(T), the user is alerted that detection ofextravasations cannot occur in step 130. An alternative method may be toset a range of acceptable differences in fluid and tissue temperaturefor asymmetric operation, thereby comparing the value of the differencebetween tissue and fluid temperatures with a negative and positivethreshold value.

In step 132, assuming that the absolute difference of the fluid andtissue temperature is above the minimal threshold, a temperaturediscrimination function, ₋₋ T_(disc), is determined based on the caseselected for the algorithm. In the case of simple temperaturedifference, ₋₋ T_(disc) is determined as follows:

    .sub.-- T.sub.disc =T.sub.s -T.sub.s.sbsb.o

where T_(s) is the current tissue temperature and T_(s).sbsb.o is theinitial tissue temperature at the beginning of the fluid injection. Thetemperature discrimination function is thus the simple temperaturedifference between the current tissue temperature and the initial tissuetemperature at the beginning of the injection.

In the case of time delayed temperature difference, ₋₋ T_(disc) isdetermined as follows:

    .sub.-- T.sub.disc =T.sub.s -T.sub.s.sbsb.t--t

where the temperature discrimination function reflects the temperaturedifference between the most recent tissue temperature and some othertissue temperature measurement taken at time t--t, which is for apredetermined interval prior to the current time. In this last instance,the processor 64 (see FIG. 2) causes a periodic series of tissuetemperatures to be stored in memory 66, from which they are sequentiallyretrieved at each time that the temperature discrimination function isrecalculated.

In the general case of the temperature discrimination function, ₋₋T_(disc) is determined as a function of tissue temperatures at differenttime increments:

    .sub.--l T.sub.disc =f(T.sub.s.sbsb.i), i=0,1,2 . . . n

Any number of temperature discrimination functions fit within thegeneral case, including first and higher derivatives of the tissuetemperature with respect to time.

The _(--T) _(disc) calculated in step 132 is compared with the initialpositive and negative alarm threshold values, R_(alarm).sbsb.--_(pos)and R_(alarm).sbsb.--_(neg), in step 140. if ₋₋ T_(disc) exceeds thepositive alarm threshold R_(alarm).sbsb.--_(pos) or is below thenegative alarm threshold, R_(alarm).sbsb.--_(neg), step 136 isimplemented such that an alarm signal is generated to warn the user thatan extravasation or infiltration has occurred. The alarm processor 62can respond by halting fluid flow from the fluid injector 54 as in step138. The alarm processor 62 may also place the injection in a hold stateso the operator may check the patient. An option may be given to restartthe injection or to override the alarm.

If ₋₋ T_(disc) is within the positive and negative thresholds in step140, new tissue and fluid temperature values are determined from antenna58 and temperature sensor 76 in step 142 and stored in memory 66. Theactual flow rate, F, is also ascertained from the fluid injector input72 in step 144 and stored in memory 66.

The alarm thresholds R_(alarm).sbsb.--_(pos) and R_(alarm).sbsb.--_(neg)are then updated in step 146 according to the case selected in step 116.In the cases of a simple temperature difference and time delayedtemperature difference, the alarm thresholds are updated as follows:

    R.sub.alarm.sbsb.--.sub.pos =Max  C.sub.1, C.sub.2 ·(T.sub.s -T.sub.f)!.

    R.sub.alarm.sbsb.--.sub.neg =Min  C.sub.3, C.sub.4 ·(T.sub.s -T.sub.f)!.

Constants C₁₋₄ are determined by clinical data. For example, they may bedetermined as a function of flow rate and vein diameter.

In the general case of the temperature discrimination function the alarmthresholds may be stated as follows.

    R.sub.alarm.sbsb.--.sub.pos =f.sub.3 (P.sub.1 . . . n, F,T.sub.s.sbsb.i, T.sub.f.sbsb.i)

    R.sub.alarm.sbsb.--.sub.neg =f.sub.4 (P.sub.1 . . . n, F,T.sub.s.sbsb.i, T.sub.f.sbsb.i)

The alarm thresholds are calculated as a function of patient parameters,P₁ . . . n, injection flow rate, F, and the tissue temperature and fluidtemperatures taken and stored for selected times. Many differentspecific algorithms may be used which are included in the above generalcase, including those which use first and higher derivatives of thetissue and/or fluid temperatures with respect to time.

After updating the alarm thresholds and tissue and fluid temperatures,the checks are performed repeatedly until the end of the fluid injectionis determined at step 124. This adaptive algorithm 110 allows thethresholds to be adjusted for changing temperatures to allow for morereliable detection. If desired, several different calculation techniquesmay be considered by the algorithm. For example, different alarmthresholds and temperature discrimination functions may be compared bythe alarm processor 62 with each other for greater reliability.

FIG. 11 is a graph of the tissue temperature and the fluid temperatureat the beginning of a fluid injection procedure. The tissue temperatureis measured by the radiometer 60 based upon calibration using a waterphantom while the fluid temperature is measured with the clip-ontemperature sensor 76. These data illustrate that the tissue temperatureand the fluid temperature may be very close in clinical situations. Asmay be seen, a fraction of the measurements lies within an initialminimum fluid/tissue difference of 1 degree Celsius. FIG. 12 is a graphof tissue temperature and fluid temperature 20 seconds after thebeginning of fluid injection.

The relatively cold temperature of the fluid T_(f) in FIG. 11 resultsfrom fluid residence prior to injection in the connector tube 48. Thealarm thresholds R_(alarm).sbsb.--_(pos) and R_(alarm).sbsb.--_(neg)will vary as a function of the value of T_(s) -T_(f). As the temperaturedifference increases, the value of ΔT_(disc) necessary to trigger analarm also increases.

As the fluid temperature warms up, reflecting the fact that the fluidbeing injected has only been in the relatively cold connector tube 48for a short time period, T_(s) -T_(f) will decrease and subsequentlyincrease and R_(alarm).sbsb.--_(pos) and R_(alarm).sbsb.--_(neg) willalso decrease and subsequently increase. FIGS. 11 and 12 demonstrate thetechnical advantage in adjusting the alarm thresholds to take fluidtemperature changes into account.

FIG. 14 is a block diagram of a fourth embodiment of the presentinvention indicated generally at 182. Like elements have numbersidentical to their counterparts in FIG. 2. FIG. 14 shows a configurationwhere a heating/cooling element 184 is attached to the connector tubing48. The heating cooling element 184 has a small mass of thermallyconductive material 186 which is embedded within a connector 188 betweenends of the tubing 48. The mass 186 allows quick heat transmission to orfrom the fluid. The mass 186 may be connected to a heater 192 via a line190 in order to be energized to heat the fluid. This arrangement allowsheating or cooling to be expedited, similar in concept to the rapidresponse of the fluid temperature sensor in FIGS. 5-7.

The fluid may also be cooled by passing a portion of the connectortubing 48 through a thermally conductive material with a large thermalmass such as an aluminum block at room temperature (not shown). Heat isdissipated from the fluid since room temperature is typically less thantissue temperature in most environments. This arrangement allows somecooling of the fluid before it is injected so that a minimum temperaturedifference between fluid and tissue temperature is achieved. The fluidmay also be heated by warming the block to some elevated constanttemperature. No measurement of fluid temperature is needed if thethermal conductivity and thermal mass are chosen large enough tomaintain a relatively consistent fluid temperature. In another approach,a thermoelectric or other heating or cooling device is attached to ablock of thermally conductive material with sizable thermal mass so thatthe fluid gains or loses heat to or from the block.

FIG. 15 is a block diagram of a fifth embodiment of the presentinvention indicated generally at 202. Like elements have numbersidentical to their counterparts in FIG. 2. FIG. 15 shows a configurationwhere a microwave antenna 204 is attached to tubing 48. The microwaveantenna 204 is coupled to a multiplexor 206 via a line 208. Themultiplexor 206 allows the microwave antenna 204 to be connected toeither a radiometer receiver 210 which is coupled to processor 62 viainput 70 or a microwave transmitter 212 via line 214. The multiplexor206 is activated and controlled by the alarm processor 62 via selectionline 216.

The microwave antenna 204 is used to measure fluid temperature whenmultiplexor 206 is selected to choose connection of the radiometerreceiver 210 via line 208. In this selection mode, the antenna 204senses fluid temperature similar to antenna 58. If the fluid temperatureneeds to be raised to allow sufficient temperature difference forextravasation detection, the multiplexor 206 is selected to a secondmode via line 216. The microwave antenna 204 then transmits energy frommicrowave transmitter 212 which causes antenna 204 to emit energy to thefluid and heat the fluid. The radiometer receiver 210 is isolated fromthe transmitter output signal when the transmitter 212 is active. Ofcourse other sensors which may be used as heating elements and sensorssuch as thermistors and metal foil heating elements where the elementcan dissipate energy as heat and the electrical resistance or some otherproperty of the same element changes with temperature to allow fortemperature sensing may be substituted for the microwave antenna 204.Additionally, separate control lines to sensors and heating elements maybe used instead of the multiplexor arrangement.

The above described fourth and fifth alternate embodiments allowsdetection of extravasations when the difference in fluid and tissuetemperatures is not sufficiently large. The algorithm described aboveneed only be modified as shown in the flow diagram in FIG. 16. FIG. 16shows a modified algorithm 200 which is similar to the algorithm in FIG.10. Like numbers represent identical steps to the flow diagram in FIG.10. As in the algorithm in FIG. 10, initial patient parameters, flowrate and case are selected or input in steps 112, 114, and 116. Aftermeasuring the initial tissue and fluid temperature in step 118 andinitializing the alarm thresholds in step 120, whether the injection hasbeen started or is complete is determined in steps 122 and 124. Thedifference between tissue and fluid temperature is then compared withthe minimal difference threshold in step 128. Like the previousalgorithm, if the difference of the fluid and tissue temperature isgreater than the minimal difference threshold, the algorithm proceeds tocheck for extravasations and update threshold values. If the differenceis less than the minimal difference threshold, the fluid temperature iscontrolled in step 202 in order to increase the difference between fluidand tissue temperature. Once the fluid temperature has been changedsufficiently, the algorithm loops back to step 118 and measures tissueand fluid temperatures.

Thus, the fluid temperature and the tissue temperature are measured andone or both may be controlled so that a minimum temperature difference,R_(min).sbsb.--_(T), of several degrees Celsius needed for reliableextravasation detection is established between the fluid and tissuetemperature. This method improves detection reliability since thecondition where fluid temperature and tissue temperature are similar isprecluded by temperature control of the delivered fluid temperature, orcontrol of tissue temperature or control of both temperatures. Thetemperature control greatly reduces the occurrences where the operatoris warned that reliable detection cannot take place because a minimumtemperature difference does not exist. This method is desirable sincesimilar temperatures are frequent during normal clinical use as mediafor CT injections and other injections is often preheated toapproximately body temperature for patient comfort before the fluid isinjected.

In order to achieve a minimum temperature difference between the fluidand tissue temperatures, both temperatures are measured and the fluid ortissue may either be heated or cooled to provide a minimum differencebetween the two. After fluid or tissue temperature is corrected toobtain a minimal threshold difference between fluid and tissuetemperature, the same extravasation detection algorithm previouslydescribed based on fluid and tissue temperature measurements may be usedin conjunction with this method. If the fluid temperature is controlledwell enough at the point close to the patient's limb, other algorithmswith fixed thresholds depending only upon flow rate may be used.Measurement or control of the fluid temperature at the point ofinjection overcomes the problems of false alarms. The steps of thepreviously described algorithm which determine and warn of aninsufficient fluid and temperature difference may remain as a check onthe proper operation of the temperature control portion of the device.

Cooling is preferable since the latitude for temperature increase ofhuman body tissue and injected fluid is limited to a few degrees Celsiusabove normal core body temperature (approximately 37 degrees Celsius),otherwise tissue damage may occur. Fluid or tissue near the injectionsite may easily be cooled by the few degrees Celsius in temperatureneeded to ensure the minimum temperature difference condition exists fordetection of extravasation. In most cases it should only be necessary toheat or cool the fluid to several degrees Celsius below or above tissuetemperature for reliable detection of extravasation to take place.

Controlling fluid temperature is preferable to controlling tissuetemperature since tissue thermal mass and conductivity may vary frompatient to patient depending on limb size, anatomy, tissue content, andcirculation influences. Fluid temperature may be controlled at thesyringe or as it is delivered through the connector tubing. At theconnector tube fluid may be cooled or heated through the use of athermoelectric or other cooling device in line or around the tubing asshown in FIG. 14. As with the fluid temperature sensor, it isadvantageous to place the heating or cooling element near the injectionsite and fluid temperature sensor, to minimize temperature measurementerrors of the estimated fluid temperature at the injection site and tominimize control lag errors from heat dissipation at the connectortubing to the ambient environment.

Another feature of the present invention is using the alarm processor 62in one operating mode, and then modifying it to operate in other modes.FIG. 13 shows a block diagram 150 of an algorithm for modifying theoperating mode of the alarm processor 62. A considerable amount of humanclinical data is needed to precisely determine the alarm thresholdsettings and algorithm for modification. Initially, the system displaysthe fluid and tissue temperatures (T_(f), T_(s)) for the operator instep 152. This may be done through a user interface on alarm processor62 (not shown). The operator can look at these data and query thepatient about pain if the traces seem abnormal. Extravasation detectiontakes place in an initial mode in step 154 using threshold values basedsolely on the fluid and tissue temperatures. In the step 156, the alarmprocessor 62 stores significant data from each injection in the firstmode 154 for subsequent retrieval and processing. Alternatively, anindependent storage device such as a database in a computer may be usedto store the significant data.

After enough data are collected from clinical sites, an alarm thresholdalgorithm can be determined and then installed in the memory 66 ofprocessor 62 as in step 158. A second mode of extravasation detection160 could use a user-selectable threshold scale mentioned above, but notuse patient-specific data to modify the thresholds.

While operating in the second mode 160, patient data would be collectedand stored as in step 162. Algorithms are then designed in step 164 toallow operation in a third mode of extravasation detection 166, wherepatient specific data influence the thresholds. The system could then bechanged to operate in the third mode 166, left in the second mode 160,or even in the first mode 154, depending upon operator preference.

The present invention is not limited to CT applications. For example,the present invention may be used to detect extravasations in any fluidinjection application such as IV injections. Such a system is notlimited to electrically driven fluid delivery pumps but could be usedwith hand driven, mechanical, or gravity driven fluid injectors (such asan IV drip bag). Additionally, one skilled in the art will appreciatethat dedicated electronic circuits may replace part or all of thealgorithm used by the alarm processor circuit to perform the variousdetection and alarm functions.

Although the present invention has been described in terms of preferredembodiments, the present description is given by way of example and isnot intended to be limiting to the scope of the invention described andclaimed herein.

What is claimed is:
 1. Apparatus for detecting extravasations in tissueinjected with fluid from a fluid injector, comprising:a fluidtemperature sensor for sensing the temperature of fluid present in aconnector tube which transmits fluid to a patient, and generating afluid temperature signal in response thereto; a tissue temperaturesensor for sensing the temperature of tissue proximate the site ofinjection and generating a tissue temperature signal in responsethereto; and a processor adaptable to periodically receive said tissuetemperature signal and said fluid temperature signal, said processorhaving an alarm circuit for declaring the occurrence of an extravasationand a threshold calculation circuit for periodically calculating atleast one threshold value as a function of said tissue temperaturesignal and said fluid temperature signal, said processor activating saidalarm circuit as a function of said tissue temperature signal, saidfluid temperature signal, and said at least one threshold value duringthe fluid injection.
 2. The apparatus of claim 1 wherein said fluidtemperature sensor is an in-line sensor mounted in said connector tube.3. The apparatus of claim 1 wherein said fluid temperature sensor is amicrowave antenna and a radiometer coupled to said microwave antenna. 4.The apparatus of claim 1 wherein said fluid temperature sensor is athermistor having a clip attaching said thermistor to said connectortube.
 5. The apparatus of claim 1 wherein said fluid temperature sensoris a thermocouple disposed adjacent said connector tube.
 6. Theapparatus of claim 1 wherein said tissue temperature sensor is amicrowave antenna and a radiometer coupled to said microwave antenna. 7.The apparatus of claim 1, wherein said processor further comprises:acircuit for deriving at least first and second tissue temperatures fromsaid tissue temperature signal at different times; a circuit forderiving a fluid temperature from said fluid temperature signal; amemory for storing said first and second tissue temperatures and saidfluid temperature; a temperature discrimination function circuit forcalculating a temperature discrimination function as a function of saidfirst and second tissue temperatures; and a comparison circuit forcomparing said temperature discrimination function with said at leastone threshold, said comparison circuit activating said alarm circuit todeclare an extravasation when the value of said temperaturediscrimination function exceeds said at least one threshold.
 8. Theapparatus of claim 7, wherein said threshold calculation circuitcalculates a first, positive threshold as a function of said secondtissue temperature and said fluid temperature, said thresholdcalculation circuit further calculating a second, negative threshold asa function of said second tissue temperature and said fluid temperature,said comparison circuit activating said alarm circuit when either thevalue of said temperature discrimination function exceeds said firstthreshold or when the value of said temperature discrimination functionis less than said second negative threshold.
 9. The apparatus of claim7, wherein said temperature discrimination function circuit periodicallycalculates the temperature discrimination function as the differencebetween said fluid tissue temperature and each of a plurality ofsequentially determined second tissue temperatures.
 10. The apparatus ofclaim 7, wherein said first tissue temperature is a tissue temperatureat the beginning of fluid injection, said second tissue temperaturebeing a current tissue temperature.
 11. The apparatus of claim 7,wherein said second tissue temperature corresponds to a current time,said first tissue temperature being taken and stored by said memory fora time which is a predetermined interval earlier than said current time.12. The apparatus of claim 7, and further comprising means for enteringat least one patient parameter, said memory storing said at least onepatient parameter, said threshold calculation circuit calculating saidthreshold as a function of said at least one patient parameter.
 13. Theapparatus of claim 12, wherein said at least one patient parameter isselected from the group consisting of age, vein condition, vein size,vein depth, health of the patient, obesity, type of vascular entrydevice being employed, vascular insertion difficulty and needlepositioning confidence.
 14. The apparatus of claim 12, wherein saidmeans for entering said at least one patient parameter is adaptable toreceive a plurality of different patient parameters, said memoryadaptable to store said plurality of patient parameters, said thresholdcalculation circuit calculating said threshold as a function of saidplurality of patient parameters.
 15. The apparatus of claim 12, andfurther comprising means for receiving a fluid flow rate for the fluidto be injected, said threshold calculation circuit calculating saidthreshold as a function of said fluid flow rate.
 16. The apparatus ofclaim 1 wherein said processor further comprises a threshold circuitcapable of taking initial tissue and fluid temperatures and calculatinga threshold value based on said initial tissue and fluid temperatures,said processor further comprising a discrimination circuit capable ofcalculating a temperature discrimination function based on said initialtissue temperature and a current tissue temperature, said discriminationcircuit further activating said alarm circuit if said temperaturediscrimination function exceeds said initial threshold value.
 17. Theapparatus of claim 16 wherein said threshold circuit further includes acircuit for determining updated fluid and tissue temperatures andacircuit for calculating an updated threshold value, said discriminationcircuit further including a circuit for calculating an updatedtemperature discrimination function and a circuit for activating saidalarm circuit if said updated temperature discrimination functionexceeds said updated threshold value.
 18. The apparatus of claim 1wherein said processor further comprises a warning circuit whichcompares the difference of said fluid temperature and said tissuetemperature with a minimal difference threshold to warn that noextravasation detection is possible.
 19. A fluid temperature sensor foruse with an extravasation detector having a fluid needle, a fluidconnector tube having fluid, and a connector having an interior sidewallconnecting said tube to said needle, said fluid temperature sensorcomprising:an electrical temperature transducer; and a thermallyconductive insert adapted to extend through said connector and saidinterior sidewall, said thermally conductive insert adaptable to be incontact with said fluid in said connector tube to provide a temperatureconductive path, and said thermally conductive insert coupled to saidthermoelectric transducer.
 20. The fluid temperature sensor of claim 19wherein said transducer is a thermistor.
 21. The fluid temperaturesensor of claim 19 wherein said transducer is a thermocouple.
 22. Afluid injection system comprising:a fluid injector head capable ofinitiating and stopping fluid flow; a connector tube coupled to saidfluid injector, said tube forming a path for transmitting fluid fromsaid fluid injector to tissue containing a vessel into which fluid isintended to be injected; a fluid temperature sensor located on saidconnector tube, said temperature sensor producing a fluid temperaturesignal representing the temperature of said fluid in said connectortube; a tissue temperature sensor for generating a tissue temperaturesignal as a function of the temperature of said tissue; and an alarmcircuit coupled to said tissue temperature sensor and said fluidtemperature sensor, said alarm circuit having a temperaturediscrimination function circuit capable of calculating a temperaturediscrimination function from said tissue temperature, a thresholdcircuit capable of comparing at least a first threshold value with saidtemperature discrimination function, said threshold circuit calculatingsaid first threshold value at different time intervals during said fluidflow.
 23. The fluid injection system of claim 22 wherein said tissuetemperature sensor further comprises:an antenna disposed to receivemicrowave radiation from said tissue; and a radiometer coupled to saidantenna, said radiometer capable of producing said tissue temperaturesignal.
 24. The fluid injection system of claim 22, wherein saidtemperature sensor is attached to a clip, said clip attaching saidtemperature sensor to said tube connector.
 25. The fluid injectionsystem of claim 23 wherein said fluid temperature sensor comprises anantenna located on said connector tube and a radiometer coupled to saidantenna for generating said fluid temperature signal.
 26. The fluidinjection system of claim 25, further comprising a multiplexor, anoutput of said multiplexor coupled to said radiometer, a first input ofsaid multiplexor coupled to said antenna located on said connector tube,and a second input of said multiplexor coupled to said antenna locatednear said tissue, said multiplexor selectively being sending saidsignals from said temperature sensor and said antenna located near saidtissue to said radiometer.
 27. The fluid injection system of claim 22,wherein said fluid temperature sensor is an electrical temperaturetransducer.
 28. The fluid injection system of claim 27, wherein saidtransducer is a thermistor.
 29. The fluid injection system of claim 27,wherein said transducer is a thermocouple.
 30. The fluid injectionsystem of claim 27, wherein said transducer is imbedded in a disposableplastic piece mounted to said connector tube.
 31. The fluid injectionsystem of claim 27, wherein said fluid temperature sensor comprises ahousing mounted to said connector tube and defining a fluid paththerethrough for fluid to be injected, said housing having an exteriorand an interior adjoining said fluid path, a heat conductor disposed insaid housing and providing a heat conductive path from said interior tosaid exterior, said transducer affixed to said heat conductor.
 32. Thefluid injection system of claim 22, wherein said alarm circuit furthercomprises a processor and a memory, said memory capable of holdinginstructions for said processor.
 33. The fluid injection system of claim22 wherein said alarm circuit is capable of controlling said fluidinjector to stop fluid flow when said temperature discriminationfunction exceeds said first threshold value.
 34. The fluid injectionsystem of claim 22 wherein said first threshold value is calculated bysaid processor as a function of said temperature of said tissue and saidtemperature of said fluid.
 35. The fluid injection system of claim 34,and further comprising means for entering at least one patient parameterand storing said at least one patient parameter, and wherein said firstthreshold value is calculated by said processor as a function of said atleast one patient parameter.
 36. The fluid injection system of claim 35,wherein said at least one patient parameter is selected from the groupconsisting of age, vein condition, vein size, vein depth, health of thepatient, obesity, type of vascular entry device being employed, vascularinsertion difficulty and needle positioning confidence.
 37. The fluidinjection system of claim 35, wherein said means for entering said atleast one patient parameter is adaptable to receive and store aplurality of different patient parameters, and wherein said firstthreshold value is calculated by said processor as a function of saidplurality of patient parameters.
 38. The fluid injection system of claim22 wherein said alarm circuit further comprises a second circuit capableof comparing said temperature discrimination function with a secondnegative threshold value, said second circuit calculating said secondnegative threshold value at different time intervals during said fluidflow.
 39. The fluid injection system of claim 22 wherein said alarmcircuit is capable of controlling said fluid injector head to stop fluidflow when said temperature discrimination function is less than saidsecond negative threshold value.
 40. A method for detectingextravasations in tissue injected with fluid from a fluid injector,comprising the steps of:periodically sensing the temperature of fluidpresent in a connector tube transmitting fluid to a patient, andgenerating a fluid temperature signal in response thereto; periodicallysensing the temperature of tissue proximate the site of injection andgenerating a tissue temperature signal in response thereto; receivingthe fluid temperature signal and the tissue temperature signal; storinga fluid temperature and a tissue temperature derived from the receivedsignals; and declaring the occurrence of an extravasation as a functionof said tissue temperature signal and said fluid temperature signalduring the fluid injection.
 41. The method of claim 40 and furthercomprising the steps of:determining initial tissue and fluidtemperatures; calculating at least one initial threshold value as afunction of said initial tissue and fluid temperatures; calculating atemperature discrimination function based on said initial tissuetemperature; and activating an alarm if said temperature discriminationfunction exceeds said initial threshold value.
 42. The method of claim41, and further comprising the steps of:determining updated fluid andtissue temperatures; calculating an updated threshold value as afunction of said updated fluid and tissue temperatures; calculating anupdated temperature discrimination function; and activating said alarmif said updated temperature discrimination function exceeds said updatedthreshold value.
 43. The method of claim 41 further comprising the stepsof:comparing the difference between said fluid temperature and saidtissue temperature to a minimal difference threshold; warning that noextravasation detection may occur if said minimal difference thresholdexceeds said difference.
 44. A method of detecting an extravasation influid injected into a tissue by a fluid injector which generates fluidflow through a connector tube, the method comprising the stepsof:measuring a first tissue temperature; measuring a first fluidtemperature; calculating a first threshold value as a function of saidfirst tissue temperature and said first fluid temperature; measuring asecond tissue temperature at a time after said step of measuring saidfirst tissue temperature; calculating a temperature discriminationfunction from said first and second tissue temperatures; comparing saidfirst threshold value with said temperature discrimination function;generating an alarm signal if said temperature discrimination functionexceeds said threshold value; measuring a second fluid temperature and athird tissue temperature; calculating an updated temperaturediscrimination function from said third tissue temperature; calculatingan updated first threshold value as a function of said second fluidtemperature and said third tissue temperature; comparing said updatedfirst threshold value with said updated temperature discriminationfunction; and generating an alarm signal if said updated temperaturediscrimination function exceeds said updated first threshold value. 45.The method of claim 44, further comprising the steps of:disposing anantenna near a tissue; coupling said antenna to a radiometer capable ofproducing a signal representing the tissue temperature; attaching atemperature sensor to said connector tube; coupling an alarm processorto said radiometer and said temperature sensor; and performing saidsteps of comparing, calculating, and generating said alarm signal. 46.The method of claim 44 further comprising the steps of:calculating asecond threshold value as a function of said first tissue temperatureand said first fluid temperature; comparing said second threshold valuewith said temperature discrimination function; generating an alarmsignal if said second threshold value exceeds said temperaturediscrimination function; calculating an updated second threshold valueas a function of said second fluid temperature and said third tissuetemperature; comparing said updated second threshold value with saidupdated temperature discrimination function; and generating an alarmsignal if said updated second threshold value exceeds said updatedtemperature discrimination function.
 47. The method of claim 44 whereinsaid step of calculating an updated temperature discrimination functionfurther comprises selecting the second and third tissue temperaturessuch that a predetermined constant interval of time is between them. 48.Apparatus for detecting an extravasation in tissue injected with fluidfrom a fluid injector, the fluid transmitted through a connector tube,the apparatus comprising:a tissue temperature sensor for sensing thetemperature of the tissue proximate the injection and generating atissue temperature signal in response thereto; a fluid temperaturecontroller for controlling the temperature of the fluid; and a processoradaptable to receive said tissue temperature signal and a fluidtemperature signal generated from the temperature of the fluid, saidprocessor having an alarm circuit for declaring the occurrence of anextravasation as a function of said tissue temperature signal and saidfluid temperature signal, said processor coupled to said fluidtemperature controller to control said temperature of said fluid in saidconnector tube so that a minimum difference exists between said tissuetemperature and said fluid temperature.
 49. The apparatus of claim 48,wherein said fluid controller further comprises a temperature sensor forsensing fluid temperature and generating said fluid temperature signal.50. The apparatus of claim 49, wherein said fluid temperature sensor isa microwave antenna and a radiometer coupled to said microwave antenna,and wherein said fluid controller further comprises a microwavetransmitter coupled to said microwave antenna.
 51. The apparatus ofclaim 49, wherein said temperature sensor is a thermistor, and whereinsaid fluid controller further comprises a heating element coupled tosaid thermistor.
 52. The apparatus of claim 49, wherein said temperaturesensor is a metal foil heating element, and wherein said fluidcontroller further comprises a heating element coupled to said metalfoil heating element.
 53. The apparatus of claim 48, wherein said fluidtemperature controller is located on said connector tube.
 54. Theapparatus of claim 53, wherein said fluid controller is a block ofthermally conductive material.
 55. The apparatus of claim 54, whereinsaid material is aluminum.
 56. The apparatus of claim 54, wherein saidfluid controller further comprises a heating device attached to saidblock of thermally conductive material.
 57. The apparatus of claim 54,wherein said fluid controller further comprises a cooling deviceattached to said block of thermally conductive material.
 58. A method ofdetecting an extravasation in fluid injected into a tissue by a fluidinjector which generates fluid flow through a connector tube, the methodcomprising the steps of:measuring a tissue temperature; measuring afluid temperature; controlling said fluid temperature so the differencebetween said tissue temperature and said fluid temperature is sufficientto permit extravasation detection; and declaring the occurrence of anextravasation as a function of said tissue temperature and said fluidtemperature.
 59. A method of detecting extravasations in tissue injectedwith fluid from a fluid injector, comprising the followingsteps:periodically sensing the temperature of fluid present in aconnector tube transmitting fluid to a patient, and generating a fluidtemperature signal in response thereto; periodically sensing thetemperature of tissue proximate the site of injection, and generating atissue temperature signal in response thereto; receiving the fluidtemperature signal and the tissue temperature signal; storing a fluidtemperature and a tissue temperature derived from the received signals;determining the initial tissue and fluid temperatures; calculating atleast one initial threshold value as a function of the initial tissueand fluid temperatures; calculating a temperature discriminationfunction based on the initial tissue temperature; and activating analarm declaring the occurrence of an extravasation if the temperaturediscrimination function exceeds the at least one initial thresholdvalue.